'But officer, the speed limit is 70 mph, can't I go 80?'

Q: As you know, the 10-over-the-speed-limit allowance is an unwritten rule permitted in Pennsylvania and in many other states. Is it likely to continue when the 70 mph law goes into effect?

— Manny Kokolis, South Whitehall Township

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Q: Regarding the state's plans to raise the maximum speed on some highways to 70 mph, people inevitably will predict mayhem and carnage on the highways. However, I expect accidents and fatalities to decrease. With millions of miles under my belt in an 18-wheeler, I'm all about safety, and setting speed limits at the 85th percentile — the rate at which 85 percent of motorists would travel without guidance — is the safest approach.

— Dave Kulp, Bethlehem

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A: In cases of motorists being "clocked" by radar or other electronic timing devices, there's a tolerance factor that's not an unwritten rule, but a black-and-white requirement of Pennsylvania law. Drivers get a 6 mph "pad" as a hedge against miscalibration or other faults in the devices. In the same regard, if an officer's speedometer is the measuring device, that instrument must have been calibrated no longer than a year before the citation.

That suggests that any 70 mph speed limit amounts to a de facto 76, and any 45 equates to a 51 mph limit. Still, the cops can't stop everyone exceeding the limit, so different grace factors apply between different officers, and at different times. As we'll find later, roadway factors and traffic conditions are the biggest variable, according to some officers.

PennDOT and the state Turnpike Commission are studying highways currently posted at 65 mph (and only those roads) to determine whether a boost to 70 would be safe and appropriate. Decisions are expected no sooner than next summer. It's conceivable, though unlikely, that no 70 mph limits will be put into place.

I think public sentiment favors raising the limit, the evidence for which lies in the simple fact of prevailing conditions most everywhere: Motorists drive faster than 55 on Route 22, and faster than 65 on the Turnpike and portions of I-78 or other interstates currently posed at 65. It's almost universal. So upping the limit to 70 on the Turnpike, where the 65 sign already graces the vast majority of the toll road, only acknowledges prevailing conditions. Same with 65 mph portions of I-78 or other interstates in Pennsylvania. Motorists who don't want to drive as fast as 70 don't have to do so: It's a speed limit, not a requirement.

While it may be true that increased speed by itself doesn't necessarily raise the danger factor significantly, there must be a tipping point — 80 mph? 85? 95? — above which the majority of motorists no longer can handle safety maneuvers effectively.

And you're right, Dave, widely varying highway speeds between different vehicles are a particular concern of traffic engineers. But isn't it likely that raising the limit will widen that gap, at least to some degree? Many people will speed up; others will change nothing.

I can't shake the intuitive notion that generally, faster is less safe. Reaction time shrinks as speed increases. Driving inherently is dangerous to some degree, so it's a judgment call: How much safety is lost at 70 mph versus 65, and how much is gained in return? I think that's what traffic engineers will be considering in the coming months.

The possibility of 70 mph highways got my colleague JD Malone to wondering whether the engineers would adjust the limit on portions of highway that lie between new 70 mph sections and adjacent lower-speed sections. It's a common motorist perception that police sometimes position their speed traps in these transition zones to snag drivers who fail to notice the change, or haven't yet eased off the gas. (The law tries to prevent this practice, but it's a weak effort, prohibiting speed traps within 500 feet of decreased speed-limit postings.)

PennDOT anticipates no such adjustments. "State law requires that whenever there is a speed reduction greater than 10 mph (e.g., 70 to 55), a 'Speed Reduction Sign' must be used," spokesman Rich Kirkpatrick wrote in an email. "PennDOT policies already provide for the use of this sign and appropriate transition lengths. … At this time, we don't foresee an issue with a transition from 70 to 55 mph. Such transitions would be well marked in accordance with the procedure outlined above."

Regarding your question, Manny, retired state police Capt. Ted Kohuth, who once roamed the highways gleefully writing speeding tickets (OK, I made up the gleeful part), said an increase to 70 mph probably would not affect enforcement decisions, which are based primarily on traffic and roadway conditions.